ABSTRACT
Background:
Bruxism is a parafunctional habit that often leads to excessive wear and tear of dental restorations. Zirconia-based crowns are increasingly used due to their superior mechanical properties and esthetic advantages.
Materials and Methods:
A total of 80 patients (ages 25–60) with diagnosed bruxism were selected for the study. Each patient received at least one zirconia-based crown. The crowns were fabricated using CAD/CAM technology and cemented with resin-based luting cement. Patients were divided into two groups: Group A (40 patients) received zirconia crowns with occlusal guards, and Group B (40 patients) received zirconia crowns without occlusal guards. The crowns were evaluated for longevity and clinical performance using criteria such as crown retention, fracture, marginal integrity, and wear on the opposing dentition.
Results:
At the end of 5 years, 92% of crowns in Group A and 80% in Group B remained functional without any major complications. Crown fractures occurred in 8% of Group A patients and 20% of Group B patients. Marginal integrity was well-maintained in 95% of Group A crowns and 85% of Group B crowns. Wear on the opposing dentition was minimal in both groups, but slightly higher in Group B. The use of occlusal guards significantly improved the longevity of the crowns (P < 0.05).
Conclusion:
Zirconia-based crowns exhibit high longevity in patients with bruxism, particularly when used in conjunction with occlusal guards.
KEYWORDS: Bruxism, crown longevity, dental restorations, occlusal guards, zirconia crowns
INTRODUCTION
Bruxism, a parafunctional activity characterized by excessive clenching and grinding of teeth, is a condition that significantly affects both natural dentition and dental restorations. It can lead to attrition, fractures, and increased wear, necessitating frequent dental interventions.[1] The prevalence of bruxism varies across populations, with studies reporting a prevalence rate of 8% to 31% in adults.[2]
Zirconia-based crowns have gained popularity due to their favorable mechanical properties, including high fracture toughness, wear resistance, and biocompatibility.[3] Zirconia’s inherent strength has made it a preferred material for patients with high occlusal forces, such as those with bruxism.[4] Unlike other ceramic materials, zirconia exhibits less brittleness and is less prone to catastrophic failure under stress, making it ideal for withstanding the adverse effects of bruxism.[5]
Despite these advantages, there is still limited data regarding the long-term performance of zirconia crowns in bruxism patients. Some studies suggest that zirconia crowns may exhibit chipping or wear over time, particularly in patients who do not use protective occlusal appliances.[6] Furthermore, there is concern regarding the wear of opposing teeth when zirconia restorations are used, particularly in cases of bruxism where occlusal forces are excessive.[7]
MATERIALS AND METHODS
Study design and participants
This prospective clinical study was conducted over a period of 5 years. A total of 80 patients (ages 25–60 years) diagnosed with bruxism were selected from the outpatient department of the Department of Prosthodontics. The diagnosis of bruxism was confirmed through clinical examination and patient history, which included signs of tooth wear, jaw muscle pain, and temporomandibular joint discomfort. Patients were required to have at least one posterior tooth in need of a crown restoration and were divided into two equal groups of 40 patients each: Group A (patients receiving zirconia crowns with occlusal guards) and Group B (patients receiving zirconia crowns without occlusal guards).
Crown fabrication
Zirconia-based crowns were fabricated using CAD/CAM technology. Tooth preparation was performed with a chamfer finish line, providing at least 1.5 mm of occlusal clearance to accommodate the zirconia restoration. Digital impressions were taken using an intraoral scanner (CEREC Omnicam, Dentsply Sirona), and the digital files were used to design the zirconia crowns using CAD software (inLab 4.2, Dentsply Sirona).
Occlusal guards
Patients in Group A were fitted with custom-made occlusal guards made of hard acrylic material. Impressions for the occlusal guards were taken using alginate impression material, and the guards were fabricated in a dental laboratory.
Clinical evaluation
The primary outcome of the study was the longevity and clinical performance of the zirconia crowns, assessed at 6 months, 1 year, 3 years, and 5 years. Longevity was defined by the absence of fracture or debonding. Secondary outcomes included marginal integrity, wear on the opposing dentition, patient satisfaction, and occlusal stability. Marginal integrity was evaluated using the modified United States Public Health Service (USPHS) criteria, where Alpha (excellent) and Bravo (acceptable) scores were deemed clinically acceptable, while Charlie (unacceptable) required intervention. The wear of the opposing teeth was assessed by measuring changes in occlusal vertical dimension using a digital caliper.
Statistical analysis
Data were analyzed using SPSS software (version 25.0, IBM).
RESULTS
A total of 80 patients (40 in Group A and 40 in Group B) were followed over a period of 5 years. Data were collected on crown longevity, fracture rates, marginal integrity, wear of opposing teeth, and patient satisfaction. The mean age of the patients was 45.6 ± 8.3 years. No patients were lost to follow-up.
Crown longevity and fracture rates
Crown longevity was higher in Group A (patients with occlusal guards) compared to Group B (patients without occlusal guards). At the end of 5 years, 92% of crowns in Group A remained intact, while 80% of crowns in Group B were still functional. Fractures were observed in 8% of the crowns in Group A and 20% in Group B.
Marginal integrity
Marginal integrity was evaluated using the modified USPHS criteria. In Group A, 95% of crowns had Alpha or Bravo scores, while in Group B, 85% of crowns received acceptable scores. Statistically significant differences were observed between the two groups (P < 0.05) [Tables 1 and 2].
Table 1.
Crown longevity and fracture rates
| Parameter | Group A (with occlusal guard) | Group B (without occlusal guard) |
|---|---|---|
| Total patients | 40 | 40 |
| Functional crowns (%) | 92% (37/40) | 80% (32/40) |
| Crown fractures (%) | 8% (3/40) | 20% (8/40) |
Table 2.
Marginal integrity
| USPHS criteria | Group A (with occlusal guard) | Group B (without occlusal guard) |
|---|---|---|
| Alpha (excellent) | 80% (32/40) | 65% (26/40) |
| Bravo (acceptable) | 15% (6/40) | 20% (8/40) |
| Charlie (unacceptable) | 5% (2/40) | 15% (6/40) |
Wear of opposing dentition
Minimal wear was observed in both groups; however, wear on the opposing dentition was slightly higher in Group B. In Group A, the mean wear was 0.3 mm, while in Group B, it was 0.6 mm at the end of 5 years.
DISCUSSION
The findings of this study demonstrate that zirconia-based crowns exhibit high longevity and durability in bruxism patients, especially when occlusal guards are used. The overall crown survival rate in this study was 92% in patients using occlusal guards (Group A) compared to 80% in patients without guards (Group B), indicating that the use of occlusal guards plays a significant role in enhancing crown longevity in bruxism patients. These results align with previous studies that emphasize the benefits of occlusal protection in minimizing the mechanical stresses on dental restorations caused by nocturnal bruxism.[1,2]
Zirconia has been recognized for its high fracture toughness and flexural strength, making it a suitable material for restorations in patients with heavy occlusal loads, such as those with bruxism.[3] However, even zirconia crowns are vulnerable to fatigue fractures over time when subjected to prolonged excessive forces, which is likely the reason for the higher fracture rate observed in Group B. Studies have also shown that bruxism can accelerate the failure of ceramic restorations due to repetitive loading,[4] which further reinforces the need for occlusal guards as a preventive measure.
Marginal integrity was significantly better in Group A, with 95% of the crowns showing Alpha or Bravo scores, compared to 85% in Group B. This finding is consistent with research suggesting that occlusal guards can help preserve the marginal integrity of restorations by reducing the frequency of crown dislodgement and marginal degradation, which are often caused by excessive occlusal forces.[5] Poor marginal integrity can lead to plaque accumulation, secondary caries, and gingival inflammation, all of which compromise the long-term success of dental crowns.[6]
Wear on the opposing dentition is a major concern in bruxism patients, particularly when hard restorative materials like zirconia are used. In this study, minimal wear was observed in both groups, but the wear was slightly higher in Group B (0.6 mm) compared to Group A (0.3 mm). While zirconia is known for its high wear resistance, it has been reported to cause wear on opposing enamel in certain cases.[7]
CONCLUSION
In conclusion, this study demonstrates that zirconia-based crowns are a reliable restorative option for bruxism patients, particularly when used in conjunction with occlusal guards. Occlusal guards significantly reduce the risk of crown fracture, preserve marginal integrity, and minimize wear on the opposing dentition, leading to higher patient satisfaction.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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